Serum samples were analysed for IgM and IgG antibodies to parvovirus by ELISA and for parvovirus B19 DNA by polymerase chain reaction (PCR) in 69 HIV-1 infected Swedish patients with anemia and in 37 HIV-1 infected subjects without anemia. In 5/69 anemic patients, parvovirus B19 DNA was detected despite the lack of IgM antibody activity to the virus. The detection of parvovirus B19 DNA was significantly correlated to the degree of anemia in the anemic patients. In two patients who had a chronic anemia, a persistent parvovirus infection was detected by PCR, but not by serology, for 1 and 1.5 years, respectively. The results suggest that persistent parvovirus infection is a rare cause of anemia, but important to identify, since the infection is potentially treatable with intravenous immunoglobulin.